Typical automotive or marine alternators generate alternating current (AC) signals in three phases, each phase leading of lagging the others by 120 degrees. Such three-phase AC power can be coupled from a generator to a power converter in two different ways: (1) a Y-configuration in which three wires each carry a different phase and a fourth wire carries a neutral reference voltage; or (2) a .DELTA.-configuration in which only the first three "active" wires are used. In applications where .DELTA.-configurations are used, the neutral reference voltage is not available. Thus, while three-phase power conversion circuits frequently employ the Y-configuration since the availability of the neutral reference terminal simplifies circuit design, both configurations are used commercially.
The prior art contains several examples of three-phase power conversion circuits. One class of these prior art circuits utilizes a familiar three-phase full-wave rectifier circuit (see, e.g., element 1 in FIG. 2 of U.S. Pat. No. 4,545,464) followed by some sort of filtering or voltage regulating circuit. The following patents represent examples from this class: (1) U.S. Pat. No. 4,545,464 to Nomura, entitled APPARATUS FOR CONTROLLING AN A-C POWER ELEVATOR; (2) U.S. Pat. No. 4,853,557 to Meier et al., entitled AUTOMOTIVE ALTERNATOR POWER GENERATOR FOR WELDING OR USE OF POWER TOOLS; (3) U.S. Pat. No. 4,184,075 to Ebersberger, entitled X-RAY DIAGNOSTIC GENERATOR COMPRISING AN INVERTER FEEDING THE HIGH VOLTAGE TRANSFORMER; (4) U.S. Pat. No. 4,992,920 to Davis, entitled REGULATED AC POWER SYSTEM ENERGIZED BY VARIABLE SPEED PRIME MOVER; (5) U.S. Pat. No. 4,270,166 to Immler, entitled CIRCUIT ARRANGEMENT FOR PRODUCING A REGULATED HIGH DC VOLTAGE FROM A THREE-PHASE CURRENT; and (6) U.S. Pat. No. 4,599,687 to Smith, entitled ELECTRICAL POWER SUPPLY FOR A MOTOR VEHICLE.
These circuits based on three-phase full-wave rectifiers have several disadvantages, among which is that the three-phase full-wave rectifier circuit does not yield a sufficiently high DC voltage, thus requiring subsequent voltage doubling stages to meet common specifications. Typical rectifier based doubler circuits generate only about 150 VDC from a 115 VAC three-phase delta connection. Numerous applications, such as typical switching power supplies require approximately 300 VDC, and such conventional switching power supplies are not easily adaptable to 115 VAC three-phase delta connections, like those often used aboard a ship.
U.S. Pat. No. 3,764,886 to Zarowin, entitled THREE-PHASE VOLTAGE TRIPLING RECTIFIER CIRCUIT, describes a relatively simple diode and capacitor circuit for providing a high DC output from a three-phase AC input. Unfortunately, the Zarowin device requires a Y- as opposed to a .DELTA.-connection.
Therefore, there remains a present need for a simple circuit capable of converting 115 VAC three-phase delta power to a nominal 300 VDC level. There exists a further need for such a device which maintains an equal loading on all three input lines. Still further, there remains a need for such a power converter utilizing a minimum number of capacitors, thereby ensuring a minimum package size.
These and other needs are satisfied, at least in part, by the invention as described broadly below and in greater detail with specific reference to a presently preferred embodiment thereof.